Archive February 2013

Unintended effect of DCD on dairy farms: Nitrification blocked in downstream freshwater ecosystems Waiology Feb 28


By Marc Schallenberg

Figure 1. Sign indicating use of dicyandiamide (DCD) on a farm. DCD is a fertiliser additive used to block natural microbial denitrification in the soil, reducing nitrate pollution from dairy farms. Eco-N is the trade name for a product containing DCD.

In many ways, the nitrification inhibitor DCD (dicyandiamide), described previously by Dr Bob Wilcock of NIWA, seems like the proverbial “silver bullet”. In some situations it reduces nitrate leaching and nitrous oxide emissions from dairy farms – two serious environmental issues resulting from the New Zealand dairy boom of the last 15-20 years. It has a low toxicity and breaks down relatively quickly (weeks to months) in the environment. No wonder it was increasingly being promoted for use on dairy pastures.

But to an environmental scientist like myself, the increasing use of DCD in the environment raises some potentially troubling questions. For example, DCD is soluble in water, so it seems likely that it could end up in places where it isn’t intended to be. Indeed, residues of the chemical have recently turned up in NZ milk. But my main concern was what would happen to beneficial natural nitrogen transformations in freshwaters if residues of DCD were to leach into wetlands, lakes and estuaries, where nitrification and denitrification are extremely important natural detoxifying and self-purifying processes.

To examine this, MSc student Ian Smith and I developed a two-pronged research project to find out 1) if DCD could be measured in surface waters of the lower Taieri Plain (Otago), where DCD is in use and if so, 2) does it have powerful effects on nitrogen cycling in waters, as it does on some dairy paddocks (Fig. 1).

Figure 2. Correlations of ammonium with DCD concentrations in stream and drain sites in the lower Taieri Plain (Otago). Dashed red lines indicate apparent DCD effect thresholds. The open circle in Jan 2009 indicates an outlier site where the high ammonium concentration did not correlate with a high DCD concentration.

Measurable residues of DCD turned up in most of the stream and drain sites sampled in the lower Tairei Plain. While we were only mildly surprised that it turned up in springtime (October and November), we were quite surprised to find it also in summertime (January), long past the usual spring application period for DCD. If DCD were to have a strong effect on denitrification in the aquatic environment we expected the concentrations of DCD in water to be correlated with the amount of ammonium in the water and with the ratio of ammonium:nitrate. The survey samples did indeed show this (Fig. 2), but this did not conclude DCD was active in the aquatic environment. We would also expect to see less nitrate relative to ammonium concentrations in runoff from DCD-treated paddocks.

So we decided to set up additional experiments to test whether DCD was altering nitrogen transformations in a freshwater system when spiked with range of DCD concentrations similar to those observed in the streams and drains of the lower Taieri Plain. We set up a closed wetland system in the laboratory, where inputs, losses and transformations of nitrogen could be measured and monitored over time. Sediments and water were retrieved from a wetland in the lower Taieri Plain and put into a large aquarium. Short lengths of drain pipe were then inserted through the water into the sediment, providing 21 sediment-water cores. DCD was added to some of the cores in different concentrations. Initially, the conditions in the cores favoured dentirification with a small but surprising increase in denitrification rates in the presence of DCD. Then conditions were altered (ammonium was added) to favour nitrification. From this point onwards, DCD strongly reduced the conversion of ammonium to nitrate in the cores, just as it does on some dairy paddocks (Fig. 3).

Figure 3. Effect of DCD on nitrate and ammonium concentrations during phases of denitrification (days 0 – 37) and nitrification (days 38 – 47) in an experimental wetland system. DCD from the initial addition had almost disappeared from the system by day 37.

As a result, this study shows that the way farmers have been using DCD results in DCD residues entering freshwater ecosystems, where it can inhibit the important natural process of nitrification. However, by blocking the conversion of ammonium to nitrate in soils, the use of DCD in paddocks should decrease the total amount of nitrogen leaching to freshwaters from dairy activities. So the effects of DCD on nitrogen cycling demonstrated in this study should mainly be of concern in waters that receive substantial amounts of ammonium from other sources. These could be anoxic groundwater inputs, inputs of sewage or other industrial wastes, or where amonium production is already naturally high.

This study is the first to examine impacts of DCD on nitrogen cycling in aquatic ecosystems and its results support the current withdrawal of DCD from use at least until these effects can be studied in a variety of aquatic ecosystems and at larger scales.

Smith, I. & Schallenberg, M. (2013). Occurrence of the agricultural nitrification inhibitor, dicyandiamide, in surface waters and its effects on nitrogen dynamics in an experimental aquatic system. Agriculture, Ecosystems and Environment 164: 23-31.

Dr Marc Schallenberg is a Research Fellow in the Zoology Department at the University of Otago.

Wetlands series wrap-up Waiology Feb 08

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By Daniel Collins

Over the past two weeks we’ve had seven articles on wetlands from across New Zealand’s research and management communities. The occasion was World Wetlands Day on February 2. The articles provided a great cross-section of analysis on how we perceive, preserve and study wetlands. Here is a summary:

Catherine Knight, from Massey University, started the series with an historical account of wetlands in New Zealand and changes in perceptions, language and landscapes.

Philip Grove, from Canterbury Regional Council, shared results of a study of Canterbury’s coastal wetlands – their composition, state, and pressures.

Shonagh Lindsay, from the National Wetland Trust, described the National Wetland Trust’s project taking shape around Lake Serpentine – the Trust’s new centre, educational facilities, and restoration efforts.

Dave Campbell, from University of Waikato, described research on the carbon balance of peat wetlands.

Daniel Collins, from NIWA, put wetlands into the water cycle, combing natural history with etymology.

Hugh Robertson, from the Department of Conservation, described the conservation of internationally important wetlands within New Zealand.

Bev Clarkson, from Landcare Research, concluded the series by giving an overview of the research on wetland restoration in New Zealand.

I hope you have enjoyed the articles and learned a lot – please tell us how you thought the series went. And if you have any questions about wetlands, requests for more articles, or your own insights, please make a note of them in the comments below – hopefully the series authors or audience members can weigh in.

Dr Daniel Collins is a hydrologist and water resources scientist at NIWA.

Progress in restoring wetlands in New Zealand Waiology Feb 07

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By Bev Clarkson

The wetland restoration handbook is available free online at

New Zealand wetlands sustain indigenous biota, improve water quality, abate floods, lock up carbon, and provide cultural, recreational, and educational resources. Despite their multiple values, more than 90% of pre-settlement wetlands have been lost. Remaining wetlands are under increasing pressure through too little water, too much nutrient, and too many weeds and pests, and many require urgent action to prevent further loss and degradation.

Landcare Research and its research partners NIWA, DOC, University of Waikato, and Waikato Raupatu River Trust have worked to deliver scientifically based guidelines, techniques, and tools to improve the management and guide the restoration of wetlands. These improve the likelihood of success in repairing complex physical–biological processes, and thus reduce the risk of wasted time or resources. Publication of our wetland restoration handbook (Peters & Clarkson 2010) represents the culmination of many years of research that involved development of best practice techniques from restoration experiments, case studies, and collaboration with wetland partners and the wider community.

Bamboo rush bog ready to be showcased to the public at the proposed National Wetland Centre, Lake Serpentine.

Restoration techniques were developed through field experiments in wetlands that have been drained, burnt, mined, invaded by weeds, or otherwise modified. These experiments include restoration of a rare and threatened bamboo rush (Sporadanthus ferrugineus) bog type at a site that is being mined for horticultural peat. When the bogs are restored using our patch creation approach, nutrient balances are improved, leading to faster growth rates, improved decomposition patterns, and increased storage of carbon. Under our technical guidance, wetland managers and community groups have introduced populations of bamboo rush and rare invertebrates to three new wetland projects at sites where the bog type once occurred – Lake Serpentine, Lake Komakorau, and Waiwhakareke Natural Heritage Park, in the Waikato. The bamboo rush bog at Lake Serpentine will be showcased as part of the soon-to-be-built National Wetland Trust’s wetland interpretation centre.

Scott Bartlam, Landcare Research, sampling a nutrient enrichment plot at Toreparu Wetland, Waikato.

Our current research focuses on determining hydrological and nutrient thresholds to maintain indigenous biodiversity and functioning. This research includes a nutrient enrichment experiment across a swamp-fen-bog wetland gradient, which indicates that high inputs of phosphorus (e.g. from fertiliser drift) can threaten our unique bog ecosystems by inhibiting the formation of peat-forming roots. Another experiment on litter decomposition shows even a small lowering of the water table in wetlands can exponentially increase litter decomposition rates. This indicates the integrity of wetlands, particularly those in extensively developed landscapes, is being threatened by on-going regional lowering of water tables. On-going drainage can also lead to significant increases in the release of carbon, thus contributing to global warming.

The goal of our research is to increase the number and success rate of wetlands being restored by providing a sound foundation for their management, monitoring, and restoration. By working alongside DOC, local authorities, iwi, and the wider wetland community we will help achieve New Zealand’s high-level goals of protecting wetland biodiversity values.


Peters M, Clarkson BR eds 2010. Wetland restoration: a handbook for New Zealand freshwater systems. Lincoln, Manaaki Whenua Press. 273 p.

Dr Bev Clarkson is a plant ecologist at Landcare Research, Hamilton, and leads the MBIE-funded Restoring Wetlands programme under contract C09X1002.

Ramsar wetlands in NZ: Why are they important and where are we going? Waiology Feb 05


By Hugh Robertson

The Ramsar Convention on Wetlands is a global environmental treaty that “provides the framework for national action and international cooperation for the conservation and wise use of wetlands and their resources”. The Ramsar Convention was established in 1971, in the city of Ramsar, Iran.

Awarua wetland Ramsar site, Southland. Source: DOC.

New Zealand became a signatory to the Ramsar Convention in 1976, in the initial cohort of members. Nowadays, there are 164 countries committed to the Ramsar Convention – a truly international community.

A key focus of the convention is to designate Ramsar sites – wetlands of international importance, and more generally to improve the management of all wetland systems. Globally, there are over 2000 Ramsar wetlands, covering 204,700,000 hectares.

The same year NZ signed the convention, our first wetland became listed as one of international importance: Waituna Lagoon, Southland (3,556 ha). Since then a further five sites have been listed (Table 1). Waituna Lagoon has also expanded to form the broader Awarua wetlands Ramsar site of 18,900 ha, our largest Ramsar site.

The NZ sites are special. The mudflats of Farewell Spit, for example, support an immense biomass of invertebrates, birds and fish – with flow on benefits across Golden Bay (and wider). Waituna Lagoon is of high cultural significance and the Firth of Thames is a critical site for migratory species (Table 1). Recognising their Ramsar status also takes account of the ecosystem services that wetlands provide society, whether in the form of fisheries production, reducing flooding or tourism (PDF).

NZ Ramsar site Known for Area (ha) Date listed
Awarua wetlands, incl. Waituna Lagoon Extensive, intact peatlands, estuary, coastal lake. 18,900 1976
Farewell Spit Expansive mudflats and sandspit, high bird diversity, migratory species. 11,400 1976
Manawatu Estuary Important feeding ground for migratory species. 200 2005
Whangamarino wetland Very large raised peat dome/swamp complex. Australasian bittern stronghold. 5,900 1989
Kopuatai Peat Dome Largest raised peat dome in North Island, peat-forming Sporadanthus (rare bog plant). 10,200 1989
Firth of Thames Shell banks, tidal mud and sand flats offer extensive feeding for wading birds and waterfowl. 7,800 1990

*For more information, see the DOC website.

The global vision of the Ramsar list is to “develop and maintain an international network of wetlands which are important for the conservation of global biological diversity and for sustaining human life”. To achieve this, the Ramsar Convention has published a strategy (PDF) that recommends the development of “national networks of Ramsar Sites… which fully represent the diversity of wetlands”.

In a NZ context, I am often asked what the value of Ramsar status is. A typical question is, “isn’t our effort better invested in improving catchment management, or developing a fully representative network of protected areas such as covenants and national parks?”

My response is that the value of Ramsar listing is to significantly increase the international and national awareness of our most ecologically significant wetland ecosystems. The long-term benefits of having elevated community and stakeholder awareness can be hard to predict, but should not be underestimated. Ramsar status may also lead to the investment of more resources from government agencies, NGOs, business partners, community groups and iwi. While Ramsar sites are not closely aligned with any particular legislation, all NZ Ramsar sites (with the exception of Manawatu Estuary) are listed in Schedule 4 of the Crown Minerals Act, and are therefore closed to mining.

The Department of Conservation has outlined future priorities for implementing the Ramsar Convention – including developing a more strategic approach to site nomination. Guidelines on what constitutes ‘internationally significant’ within a NZ context are in review.

Ramsar sites in waiting. Wetlands such as those within O Tu Wharekai (Ashburton Basin) may make complementary additions to the Ramsar network. Source: H. Robertson (DOC).

Once a site becomes a Ramsar wetland, maintaining their condition is a priority. DOC recently produced a national report summarising the condition of our six sites. Overall, there was little change in their ecological state over the past four years. Some wetlands showed improvement, for example through wide-scale invasive plant control, while others (Whangamarino, Waituna Lagoon) were under threat from declining water quality [1][2]. Initiatives such as the DOC Arawai Kakariki wetland restoration programme [3] and the efforts of community groups continue to help maintain these internationally significant ecosystems.

World Wetland Day provides an opportunity to recognise the successes of what Ramsar has achieved since 1971, and to reflect on both the positive and challenging issues relating to water management. For me, this includes recognition that New Zealand has come a long way since becoming a signatory to the Ramsar Convention in 1976, and an appreciation that 164 countries are able to reach agreement on global issues such as climate change and water (PDF) – yet recognising that many of our freshwater ecosystems remain under threat.


[1] Blyth, J.M. (2011). Ecohydrological characterisation of Whangamarino wetland.Master of Science (MSc) Thesis, University of Waikato.

[2] Robertson H.A. and Funnell E.P. (2012). Aquatic plant dynamics of Waituna Lagoon, New Zealand: trade-offs in managing opening events of a Ramsar site. Wetlands Ecology and Management 20: 433-445.

[3] Robertson H. and Suggate R. (2011). Arawai Kakariki wetland restoration programme 2007-2010: Implementation report. Department of Conservation, Christchurch.

Dr Hugh Robertson is a wetland ecologist with the Department of Conservation. He is the STRP (Science and Technical) National Focal Point for the Ramsar Convention in NZ.

What makes wetlands wet lands? Waiology Feb 04

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By Daniel Collins

The simple answer is, of course, water. But that says little about the natural history of wetlands, or what physical conditions are necessary to maintain, restore or even engineer them. For that, we need to take a closer look at wetland hydrology.

Wetlands are tracts of land that are water-logged at least seasonally. They may be spongy bogs, mountain tarns, verdant swamps, or many other types. They remain wet because the inputs of water from rain, rivers or groundwater compensate any losses.

The various types can be distinguished based on their hydrology. In their book on wetland restoration, Bev Clarkson and Monica Peters (2010) quantify this continuum with the “gumboot test”. Short “red bands” are usually okay for keeping you dry in bogs, taller gumboots are needed for fens, thigh waders for swamps, and waist waders for marshes.

The continuum of wetland types in New Zealand, after Clarkson and Peters (2004).

A kettle hole at O Tu Wharekai/Ashburton Lakes. Kettle holes, formed by glacial deposits, are fed by rainfall and groundwater and can fluctuate from wet to dry depending on groundwater levels. (Photo: M. Beech, DOC)

Controlling this water balance are climate, geomorphology and even the vegetation itself. Wetlands typically form in gently sloping or topographically convergent portions of a landscape, where surface and ground waters meet. The vegetation plays several roles here, including the build-up of peat, changing evaporation and water flows, and by controlling erosion and hence the shape of the local landscape to some degree. Kettle holes, such as those in the Ashburton Lakes, are an example of the climate and glacial geomorphology controlling the hydrology, which in turn controls the ecology.

Each plant species is adapted to a particular range of wetting and drying. Too dry for too long, and terrestrial plants can invade. This is particularly important to bear in mind when conserving, restoring or engineering wetlands. It’s not enough to simply add water – the hydrological regime must match the desired ecosystem’s needs.

Some of the hydrological effects of wetlands are in essence also ecosystem services – benefits conferred to society by the wetlands. Reducing flooding and augmenting low flows are two services often cited, though they are not true for all wetlands (Bullock and Acreman, 2004). Science is actually a little in the dark as to which biophysical features of wetlands confer or degrade the various hydrological services.

And as we consider the hydrological origin of wetlands and differences between wetland types, it is also interesting to consider the etymological origin of wetland words. The word “swamp”, for example, can be traced back to the Old Norse word for “sponge”, sharing a common ancestry with “sump”. “Marsh”, “morass” and possibly “moor” have origins in the Proto-Germanic word for “sea”, and are in turn related to the words “marine” and “maritime”. “Mire” comes to us from the Proto-Indoeuropean (PIE) word for “damp”, and shares this root with “moss” and “must” (as in “musty”). “Bog” came to us via Gaelic, with a meaning of “soft” or “moist”, and earlier still from the PIE word for “bend” (as does “bow”). And lastly “fen”, which remains truest to its roots, goes back to the PIE word for “swamp”.

Ordering these words on a scale from less to more wet, in terms of their etymological roots, we get: bog – fen/swamp – mire – marsh. As a testament to biophysical basis of words, this aligns nicely with the order of wetland types illustrated above.

Much, however, remains to be learned about the hydrological origins, needs and impacts of wetlands. Continued research in this front will assist in conservation and restoration, the use of ecosystem services, and in the broader understanding of the water cycle – all very useful as NZ seeks to balance resource use with environmental protection.


Bullock A. and Acreman M. (2003). The role of wetlands in the hydrological cycle. Hydrol. Earth Syst. Sci., 7, 358-389, doi:10.5194/hess-7-358-2003.

Clarkson B. and Peters M. (2010). Wetland types. In B. Clarkson and M. Peters, eds., Wetland restoration: A handbook for New Zealand freshwater systems. Manaaki Whenua Press, Lincoln. Pp. 273.

Dr Daniel Collins is a hydrologist and water resource scientist at NIWA.

Happy World Wetlands Day! Waiology Feb 02

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By Daniel Collins

Halfway through Waiology’s series for World Wetlands Day we’ve already learned a lot about New Zealand wetlands and efforts to study and restore them. But today being the day, how about you actually visit one? I’ll be at Christchurch’s Travis Wetland. And then come back for more articles in the coming week. In the meantime, here is a buoyant cartoon from Ramsar.

Dr Daniel Collins is a hydrologist and water resources scientist at NIWA.

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